1. Field of the Invention
The present invention relates to a control device and a control method of a control valve which is used for an intake air (an intake air-gas) system of an engine. The device is provided the control valve which is an intake air throttle valve provided in the intake air-gas system provided in the intake air-gas system of the engine to control the flow rate of intake air to the engine, oran EGR valve provided in the intake air-gas system of the engine to control the flow rate of EGR gas to the engine; and                a control unit which determines a target opening of the control valve used for an intake air-gas system, in response to the operation conditions of the engine, and controls the opening of the control valve used for an intake air-gas system so that the opening conforms with the target opening.        
2. Description of the Related Art
As a technology reducing NOx in the exhaust gas emitted from an internal combustion engine, an exhaust gas recirculation device (hereafter abbreviated as an EGR device) is known. In the EGR device, a part of the exhaust gas in the exhaust gas passage is extracted as an EGR gas; the EGR gas is returned to an intake air passage through an EGR passage. Hence, when the EGR device is used, a mix of fresh intake air as well as a part of the exhaust gas, namely, an EGR gas is led into a combustion chamber.
The EGR device as described above is provided with an EGR control valve; the opening of the EGR control valve is controlled and the flow rate of the EGR gas returned to the intake air passage is controlled.
When the EGR control valve in the EGR device becomes out of order, the flow rate of the EGR gas returned to the intake air passage cannot be controlled. Thus, there may arise an apprehension that: the flow rate of the EGR gas becomes in surplus or shortage; or, the flow of the EGR gas is stopped.
Hence, various technologies in which a malfunction of the EGR control valve can be diagnosed have been proposed.
For instance, JP1998-122058 discloses a technology in which it is judged that the device including an EGR control valve is out of order when the device confirmed that a detected actual valve opening does not change in response to the target valve opening, while the device is detecting the actual valve opening by use of an actual valve opening detecting means. Hereby, the actual valve opening changes according to the change of the target opening after the target opening begins changing in a case where an EGR operation condition under which the target opening of the EGR control valve changes over a predetermined value holds.
Further, JP2007-255251 discloses an exhaust gas recirculation device as shown in FIG. 18, the device having: an EGR control valve 102 provided with a valve shaft 102b; a driving means 106 in which a reciprocating shaft 112 arranged on a line extended along the valve shaft 102b performs a to-and-fro movement in the axis direction; and, a control means (not shown. The exhaust gas recirculation device is configured so that the reciprocating shaft 112 of the driving means 106 opens the EGR control valve 102 by pressing an edge point of the center axis of the EGR control valve 102, and the control means judges the occurrence of the malfunction of the EGR control valve 102 by the magnitude level of a duty ratio of the control signal oscillated toward the driving means 106 from the control means.